A number of previous proposals have been made which provide systems for transporting magnetic tape cartridges and cassettes (hereinafter generally referred to as cartridges unless otherwise specified) between tape recording and playback units and a store of cartridges where a plurality of these cartridges is maintained. Some of these previous proposals provide for sequentially delivering cartridges to a recording and playback unit in a fixed order. Others provide for preselecting the sequence in which the cartridges are delivered to the recording and playback unit.
In order to achieve sequential delivery, whether in a fixed or selectable order, it has been previously proposed to provide for movement of the record and playback unit relative to the store of cartridges so that any selected cartridge can be conveyed in a single plane between its storage location and the record and playback unit. Such a proposal has been embodied in an audio cassette record and playback unit which is manufactured by Sony as their MTL10 product. This unit provides storage for ten audio-type cassettes maintained in parallel vertical planes and transportable each to a location, in any preselected sequence, whereat the cassette is entrained by an automatically movable holder and movable in its own plane to the record and playback unit.
Such a system is eminently suited to audio cassette record and playback units in which the reels are of light weight and are arranged to be driven by rotatable spindles. However, magnetic tape cartridges of the type which are intended for use in storage of digital information in the computer industry require to be used and driven whilst maintained in horizontal attitude due to the requirement for very precise alignment of the tape in handling rapid transfer of high density data to and from the tape.
One form of tape cartridge for use in data processing equipment is disclosed in U.S. Pat. No. 3,692,255, and a commercial form of this type of cartridge is available from Hewlett-Packard Company as its 9164-0127 600-feet magnetic tape cartridge. A characteristic feature of this cartridge is that drive is imparted to the tape reels by an endless belt frictionally engaging a drive wheel having a part of its periphery arranged to frictionally engage a drive roller of a cartridge drive unit, when the cartridge is properly mounted in the unit.
One type of cartridge record and playback unit designed for use with the aforesaid cartridge is the Hewlett-Packard Model 9144 manufactured by Hewlett-Packard Company. A similar unit is incorporated in Hewlett-Packard's Model 7900 Series tape and disc drive. With this type of tape/disc drive, when it is desired to transfer, or "dump" more data from a disc than can be stored on a single cartridge an operator has to be in constant attendance when it is desired to `dump` data from a disc onto tape storage, because it is necessary with the different storage capacities of the disc and the tape, to change tape cartridges regularly, at intervals as short as approximately every thirty minutes. It is, therefore, desirable to provide means whereby a plurality of cartridges can be transported one at a time and in any desired sequence to the record and playback unit from a store so that data can be transferred between a disc and the plurality of tapes.
The aforementioned prior art proposals are unsuitable for this purpose, either because they require the cartridges to be mounted vertically or they require either the record and playback unit or the store to be bodily movable. The net effect of the latter problem is to require very considerable re-design of existing equipment, to accommodate, inter alia, space for movement of the record and playback unit or the store.